1. Field of Invention
The present invention relates to an inspection method for correction pattern. More particularly, the present invention relates to an inspection method for comparing the original pattern to the optical proximity correction (OPC).
2. Description of Related Art
Photolithography plays an important role in the semiconductor process. For each semiconductor device, patterns of all films and doping regions are decided by this step. Therefore, the numbers of photolithography required for a process, which is the needed mask number, decide the difficulty of the process.
The photolithography technique is complicate but the principle behind it is fairy simple. For example, photosensitive material is first coated on the wafer. Then, light source is projected to the photosensitive material through the mask, which is mainly composed of glass. The light beam through the mask has the same pattern as the mask so that the mask pattern can be transferred to the photosensitive material on the wafer. The photosensitive material can be, for example, photoresist. Then, after exposure or/and development, equal or complementary pattern on the mask can be transferred to the photosensitive material. If the photosensitive material is positive photoresist, it will obtain an equal pattern as the mask. On the other hand, if the photosensitive is negative photoresist, it will obtain a complementary pattern as the mask.
As negative photoresist is used, after exposure and during the step of development, developer will go in-between the molecular of the negative photoresist. Consequently, the photoresist swells and the differentiation between the after-development pattern of negative photoresist and the mask pattern increases. It is therefore not suitable for process down to 3 .mu.m to use negative photoresist. As a result, positive photoresist is more widely used to the sub-micron semiconductor technique presently.
The exposure technique used for transferring patterns form the mask to the photoresist has three main types: contact type, proximity type and projection type. For the semiconductor technique of deep sub-micron, the degree of precision of the exposure technique is highly limited to photo-resolution. The limitation of photo-resolution may cause error or even failure of pattern transferring. Proximity exposure technique is taken as an example. FIG. 1 illustrates the original mask pattern. After the step of exposure, the pattern of photoresist is substantially the same as the pattern shown in FIG. 2. Comparing the original mask pattern in FIG. 1 and the transferred pattern in FIG. 2, the difference between these two patterns is obvious. For example, the two terminals 10, 12 of the original mask pattern shrinks to becomes terminals 20, 22 after transferred. Also, the configurations of the corners do not correspond with the original pattern but become curved. After exposure, the outer corner 14 shrinks to become a curved shape 24 and the inner corner 16 shrinks to become a curved shape 26.
The problems coming after the error due to pattern transfer is serious. For example, during the back-end processes, the error may cause over-etching and improper coupling of interconnection.
Consequently, during the process of proximity pattern transfer, the original pattern is usually processed through optical proximity correction to form a pattern for transferring. FIG. 3 shows a pattern after optical proximity correction, which has complementary pattern at the shrinking terminals. The complementary pattern at the shrinking terminals is so-called "end-cap". The pattern after optical proximity correction also has complementary pattern at the outer corners and the inner corners. However, the optical proximity correction pattern is a hypothetical pattern, which may also cause improper pattern transfer. Especially nowadays the requirement of precision keeps increasing so even trivial error can influence greatly.